1. Field of the Invention
The present invention relates to a PWM signal output circuit.
2. Description of the Related Art
With respect to a motor drive circuit configured to drive a motor while changing a current of a motor coil in a gradual manner, a BTL (Bridged Transformer Less) system motor drive circuit and a motor drive circuit configured to perform soft switching are known (see, e.g., Japanese Laid-Open Patent Publication No. 2007-37387 and Japanese Laid-Open Patent Publication No. 2004-153921).
In the BTL system motor drive circuit disclosed in Japanese Laid-Open Patent Publication No. 2007-37387, since high-accuracy operational amplifier, etc., are generally required to be used, the circuit size becomes large.
On the other hand, in the motor drive circuit configured to perform soft switching disclosed in Japanese Laid-Open Patent Publication No. 2004-153921, a soft-switching period for changing a drive current of the motor coil in a gradual manner is constant. Thus, in such a circuit, when the rotation speed of the motor decreases, the ratio of the soft-switching period out of the period during which the motor is driven becomes small. Therefore, it becomes difficult to change the drive current in a gradual manner.